1. Field of the Invention
This invention relates to a disk unit, and more particularly to a magnetic disk unit having a spindle rotating at a high speed of not less than 4000 rpm, and a housing structure suitable for providing a high-speed (about 10 ms) positioning system.
2. Description of the Prior Art
In a conventional disk unit, a housing is divided by a plane in parallel with a spindle passing through the surfaces of disks, and the spindle and disks and an actuator are inserted through the dividing plane into the divisional housings as disclosed in Japanese Patent Laid-Open Nos. 182077/1985 and 101772/1985. These publications disclosing the known techniques show that a seal is provided between the contact surfaces of the divisional housings so as to shut off the interior of the housing from the outside air.
According to the conventional techniques described above, the housing is divided by a plane in parallel with the spindle passing through the surface of a disk in spite of the necessity of supporting the spindle and a rotary shaft of the actuator at both ends thereof on the walls of a highly rigid housing. Therefore, the side walls supporting the ends of the spindle and rotary shaft tend to deflect in the direction of the spindle, and it is difficult to maintain the relative position of and the relative distance between the axes of the spindle and actuator at predetermined levels. Consequently, the relative displacement, which occurs due to the variation of the ambient temperature, of a plurality of magnetic heads and the recording tracks thereon causes a decrease in the reliability of the reading and writing capability of the disk unit.
Since the side walls mentioned above are sealed hermetically with the second divisional housing, which is opposed to the first divisional housing via the seal, the heat occurring in the spindle and actuator is rarely transmitted to the second divisional housing. As a result, a difference occurs between the temperatures of the interior of these two divisional housings, so that the thermal displacement referred to above is accelerated. Moreover, since the rigidity of the side walls supporting the spindle is low, the side walls cannot with stand the force generated by the high-speed (not less than 4000 rpm) rotation of the spindle and disks and transmitted thereto. This adversely affects the positioning accuracy of the actuator.
According to the conventional techniques, a magnetic disk is set on a spindle after the servo information has been written thereon. Therefore, when the spindle inclines, the servo track becomes eccentric in many cases.